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Electronic termination


As with any precision electronic device, proper mounting and electrical termination is necessary for trouble-free and reliable operation of an UltraVolt high-voltage power supply (HVPS). Improper electrical termination of UltraVolt HVPSs can cause damage to the electrical connectors of the power supply, resulting in the power supply’s failure. Improper mounting of the UltraVolt HVPS can create stresses (both thermal and mechanical) within the HVPS, possibly shortening the operation life of the device.

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                                   Electrical Termination & Mounting Configurations
                                                                 of UltraVolt HVPSs
As with any precision electronic device, proper mounting and electrical termination is necessary
for trouble-free and reliable operation of an UltraVolt high-voltage power supply (HVPS).
Improper electrical termination of UltraVolt HVPSs can cause damage to the electrical connectors
of the power supply, resulting in the power supply’s failure. Improper mounting of the UltraVolt
HVPS can create stresses (both thermal and mechanical) within the HVPS, possibly shortening
the operation life of the device. For more information on mounting as it relates to thermal
considerations, please see Application Note #6, “Thermal Management of UltraVolt HVPSs.”
Electrical Termination Methods of UltraVolt HVPSs
An UltraVolt HVPS is usually electrically terminated via a printed circuit board (PCB), a wiring
harness, or a combination of the two (a sub-assembly PCB) depending on the mechanical
mounting method used. Mechanical mounting methods and design considerations are discussed
PCB Termination
When an UltraVolt HVPS is electrically terminated to a PCB, there are essentially two methods of
actual termination: 1) soldering the UV HVPS directly to the PCB and, 2) using a single or dual socket
(depending on the model of HVPS utilized). Each method has its advantages and disadvantages;
however, using a socket for termination may be preferred for a field-repairable system.
The UV HVPS can easily be soldered directly to a PCB, since the pin spacing is compatible
with the 0.100”/0.200” industry-standard header spacing. This method offers ease of manual
mounting; however, it may suffer from service-related and automated-assembly drawbacks. As
discussed below, soldering the UltraVolt high-voltage power supply directly to the PCB does
not replace the mechanical mounting requirement of the HVPS. In all cases, the UltraVolt high-
voltage power supply must be mounted mechanically via one of the methods outlined below.
Sockets are the preferred connection method to UV HVPSs for several reasons. Socket
termination greatly improves your ability to troubleshoot your product, allowing for the simplified
testing of the UltraVolt high-voltage power supply and associated interface circuitry. Socketed
connections also make your product more field repairable, allowing the failed interface circuit
board or the failed HVPS to be replaced individually (permitting component level repairs).
Socketed connections are also more easily wave soldered or infrared re-flowed, since the
relatively large mass of the HVPS need not be present during either of these delicate operations.
There are essentially two options for the PCB termination of UV HVPSs: in-line machined
sockets, or press-in sockets. An example of an in-line machined socket is the 7-pin, single-row
Samtec SS-113-T-13 (see the “UltraVolt HVPS Industry-Standard Mating Connectors” guide for
more information on UltraVolt high-voltage power supply connector compatibility with different
suppliers’ products). In-line machined sockets can be handled and placed like standard electrical
components, a definite advantage over other methods of electrical termination. Press-in sockets
usually come in the form of single-pin sockets that are pressed into, then soldered directly to
the PCB. Although these sockets require nonstandard-size PCB holes and special assembly
procedures, this method requires only one type of socket (with certain HVPSs), whereas at least
two different types of in-line machined sockets would be required for a design using the more

UltraVolt, Inc.                                  AP-3
specific in-line machined sockets.
Should a UV HVPS be mounted onto a PCB (as opposed to being mounted onto a chassis),
various thermal considerations will arise. For a full discussion of the thermal considerations
in the various mounting methods of the UV HVPS, please see Application Note #6: “Thermal
Management of UltraVolt HVPSs.”
Wiring Harness Electrical Termination
The use of a wiring harness has the obvious advantage of enabling you to mount the UltraVolt
HVPS anywhere within your chassis, allowing for both optimal positioning of the UV HVPS for
thermal considerations and minimization of overall chassis size. Again, there are two choices for
the electrical termination of the HVPS: directly soldering the wiring harness to the UV HVPS or
utilizing sockets that match the plugs on the UV HVPS.
As noted previously, sockets are preferred over direct soldering for troubleshooting, field
reparability, and relative ease of assembly. However, when soldering leads directly to the UV
HVPS, remember to use a reliable method of soldering (such as ‘j’ hooking the leads around the
HVPS pins). Also keep in mind, the pins of the UV HVPS are high-quality, gold-plated, bronze-
phosphor material. Due to this material’s nature, the pins cannot sustain large lateral forces
without damage or fatigue and eventual failure. Therefore, it is recommended that the wiring
harness be strain-relieved before connecting to the HVPS. In fact, all wiring harnesses should be
strain-relieved before reaching the HVPS pins. The types of wiring harness sockets which can be
used are summarized in the “UltraVolt HVPS Industry-Standard Mating Connectors” guide (listed
under Type as ‘wire applied’).
General Rules of Thumb for Electrical Terminations to UltraVolt HVPSs
Although not yet discussed, the gauge of the wire (or the cross-sectional area of the copper
track on a PCB) feeding the UltraVolt HVPS is very important. A power supply wire of too thin a
gauge can not only cause wiring failures, but also degrade the load regulation and linearity of the
UltraVolt HVPS. How thin is too thin? As seen in Table 1 below, certain UltraVolt high-voltage
power supplies can draw up to 13 amps through the input-power pins. Table 2 can be used as a
rough guide to determine the required input-supply wire gauge, based on the UV HVPS current.

                      UV Power Supply Rating           Maximum Current

                           4W (for 12V unit)                 0.5A

                         15W / 20W (24V unit)                 1A

                                     60W                      3A

                                 125W                         6A

                                 250W                        13A

                      Table 1: A partial list of HVPSs and maximum currents
                     (See product-specific data sheets for more information.)

                                                AP-3                                                  39
UltraVolt, Inc.
                    Maximum Continuous Current        Suggested Wire Gauge
                             (Amps)                        (Gauge (AWG))
                               20                                10
                               15                                11
                               12                                12
                                8                                14
                                5                                16
                                3                                18
                                2                                20
                               0.8                               24
                               0.5                               26
                               0.3                               28
                               0.2                               30
                              Table 2: A list of HVPS currents and
                            recommended input-supply wire gauges.

Not surprisingly, choosing a PCB track size is slightly more complex than choosing a specific
wire gauge, given a particular current. In PCB applications, the maximum allowable temperature
rise of the track becomes an important design consideration. Table 3 is a general guide for the
current-carrying capacity of different external, plated-PCB track sizes.

                                              Current-Carrying Capacity
 PCB track size              0.5A                1A              1.5A                    2A
   1oz. copper           20 mils width        50 mils           100 mils              50 mils
  (1.4 mils high)      (10°C temp rise)   (10°C temp rise)  (10°C temp rise)      (45°C temp rise)
    2oz. copper            10 mils            25 mils             50 mils             25 mils
     (2.8 mils)        (10°C temp rise)   (10°C temp rise)    (10°C temp rise)    (45°C temp rise)
    3oz. copper            7.5 mils           19 mils             38 mils             19 mils
     (4.2 mils)        (10°C temp rise)   (10°C temp rise)    (10°C temp rise)    (45°C temp rise)

                  Table 3: Plated-PCB track sizes and currents with temperature rise

As Table 3 illustrates, PCBs cannot handle large currents unless proper track width and copper
weight are used. (For example, PCB-mounting a 125W unit is only recommended when specific
care is taken — such as a 3oz. copper PCB with two 75-mil tracks to the two power pins.) Please
note, a 10°C temperature rise is quite acceptable; however, a 45°C temperature rise is not
recommended for continuous use. Track width should be increased to carry the current and to
reduce self-heating.
Another important point concerns the presence of multiple pins for the same apparent function.
A perfect example is the paired Input Power Ground Return pins (#1 and #8) on the 125W “C”

UltraVolt, Inc.                                  AP-3
Series. This supply will draw up to 6 amps from the input voltage supply; however, the connector
pins are rated for a maximum of 5.9 amps. For this reason, on the 125W “C” Series, UltraVolt
paired the supply pins, increasing the rating to a total of 11.8 amps, leaving a larger margin for
safety. In order to eliminate possible damage to the HVPS’s pins, each pin of the same function
should be externally wired in parallel to spread the current over the required number of pins.
As an aside, the 250W “C” Series will draw up to 13 amps; therefore, the units utilize an
AMP mate-and-lock connector, which is rated for 10 amps per contact and 20 amps total for
the parallel connection. This connector can easily handle the relatively large currents most
likely to be supplied by an off-line switching power supply elsewhere within the chassis. If you
intend to mount a PCB on the top of a chassis-mouted 250W unit, please contact UltraVolt
Customer Service for the appropriate part-number suffix to specify the PCB power connector
with .045” square pins. Also keep in mind, although the HVPS pins labeled Input Power Ground
Return, Signal Ground Return, and HV Ground Return imply a similar function, they are not
interchangeable and each should be used only for its own purpose (see Application Notes #1 and
#16 for more information).
Mounting Configurations of UltraVolt HVPSs
Different mounting configurations are required for different models of UltraVolt high-voltage power
supplies. In all cases, supplementary mounting procedures are required. Under no circumstances
should the UV HVPS be restrained by its pins alone (the pins cannot withstand lateral shock and
will shear if the system is dropped or subjected to long-term vibration).
There are essentially two mounting configurations for low-power UV HVPSs: chassis mounting
and PCB mounting. However, certain case configurations lend themselves more to one mounting
method than to the other. High-power units (such as the 125W “C” Series) and lower power units
with the -C option have aluminum cases incorporating mounting ears or studs, making them ideal
for chassis mounting. Lower power, Mu-metal-shielded, or plastic-enclosed units (i.e. a 4W “A”
Series HVPS) have the option of being PCB mounted or chassis mounted (using an optional
mounting bracket or -E plate).
Mounting Units With Built-In Mounting Ears or Studs
As mentioned above, metal-enclosed units with built-in mounting ears or studs should normally
be chassis mounted. As many of these aluminum-enclosed units are of relatively high wattage,
chassis-mounting makes sense because it allows the produced thermal energy to dissipate easily.
For further discussion on thermal considerations, see Application Note #6 on thermal management.
When mounting units incorporating mounting ears (such as the “A” Series units with the -C or -E
option), it is good policy to use all 4 mounting holes. This ensures a lower thermal resistance, as
well as adequately restraining the relatively large mass of the metal-encapsulated UV HVPS.
Units with mounting studs (such as the High Power “C” Series) should be mounted to ensure
each stud can be utilized. Each stud should be held to the chassis using a lock washer and a #8
nut tightened to approximately 8 ftolbs of torque. The nuts should be alternately tightened in an
X-pattern to prevent possible harmful mechanical stress to the HVPS case.
In tight mounting locations where you would like to chassis-mount a -E UltraVolt, you might
consider putting a louver or tab in the chassis to lock in the inaccessible end of the HVPS, while
still bolting the opposite end to the chassis (see below).

UltraVolt, Inc.                                 AP-3
Mounting Units without Mounting Ears or Studs
Units without mounting ears or studs can be PCB mounted or chassis mounted, whichever
is preferred.
Should the UltraVolt HVPS be PCB mounted, the HVPS should be held in place using #2 screws
threaded into the HVPS’s two molded-in thermal standoffs. These screws should brace the
HVPS to the PCB, ensuring both a solid electrical connection to all pins and a firm mechanical
connection between the PCB and the UV HVPS. If these screw holes are not used, the HVPS’s
electrical pins may shear when the unit is placed under severe mechanical stress.
As noted above, these units may also be chassis-mounted using an optional bracket (for 4W to
30W units). Depending upon the height of the HVPS used (check product data sheets), either
the 0.8”-high BR-001 bracket or the 0.9”-high BR-002 can be used to fasten the UV HVPS to
the chassis wall. The bracket is fastened to the chassis using screws. The UltraVolt high-voltage
power supply is fastened to the bracket by two #2 screws threaded into the blind screw holes
in the connector side of the HVPS. Mounting the HVPS this way allows for a good thermal
interface between the power supply and the chassis wall (thus allowing the chassis to become
an alternative to a separate heat sink). This also secures the HVPS mechanically. Should the
chassis be used as a means to cool the HVPS, a thermal-resistance-reducing interface (such as a
thermal elastomer or thermal grease) should be used between the HVPS and the chassis wall. As
mentioned previously, thermal management considerations are outlined in Application Note #6.
In lower power, chassis-mount applications an alternative to mounting brackets and plates is
available. Since thermal interfacing is less critical, the HVPS can be mounted using a double-
sided foam tape with an acrylic adhesive. These tapes are rugged enough to be used in harsh
applications such as aircraft manufacture. 3M Scotch® brand VHB4929 tape has undergone
extensive testing and has been found to be a low-cost, low-labor assembly solution. It is essential
this mounting system not be used in applications where high thermal resistance would allow an
HVPS to overheat. For this reason, the tape mounting system should only be used with 4 watt
While thermally conductive acrylic tapes are available, they are not generally used as the
only mounting method for devices that weigh more than 1 or 2 ounces and are, therefore, not
appropriate for use as the only method of mounting an UltraVolt HVPS.

                                                Rev. G
UltraVolt, Inc.                         ©1992-2009 UltraVolt, Inc.

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